Pyrotechnic inflator devices utilizing solid combustible gas generant compositions are well known for use in motor vehicles such as automobiles to protect the operator thereof from injury occurring as a result of a collision between the subject vehicle and another object. An important consideration involved with installing such passive restraint systems, however, is how to arrange and position the device upon the steering wheel assembly thereof.
For reasons of styling and consumer acceptance, as well as not interfering with the driver's movement or his vision of the instrument panel, and so as not to degrade the vehicle's steering dynamics, it is desirable to arrange a crash restraint apparatus as conveniently as possible, and yet have it positioned so that it effectively accomplishes its intended protective function. In addition, since an inflator device for such a crash restraint system must be capable of discharging a relatively large volume of gas in a very short period of time (i.e., within about 30-60 milliseconds), there are safety considerations which must be taken into account, not only in the deployment of the inflator within the vehicle, but also with regard to handling, installing, replacing and repairing such devices.
Moreover, in the particular case of a driver's side, i.e., steering wheel, installation within an automobile or a truck, for example, the utilization of an inflator apparatus having a relatively low mass is important for several reasons. First, the steering wheel assembly is installed in a cantilevered position at the end of the steering column, and thus excessive weight placed upon this assembly can cause column whip, attributable to vertical accelerations due to road shocks (e.g., bumps or chuckholes) which may, in turn, lead to degraded if not total loss of driver control. Secondly, if for reasons such as styling or driver vision line clearance, the inflator is required to be located asymmetrically with respect to the steering column centerline, any excessive weight attributable to this device will create resistive wheel turning torque, thus degrading the rotational dynamics of the steering assembly and providing potential for loss of driver control or other undesirable vehicle handling "feel" under certain driving conditions.
Driver's side airbag inflator assemblies are thus conventionally centrally located within the circumferential periphery of the vehicle's steering wheel. Typically, the terminal portion of the steering shaft adjacent the steering wheel is covered by a steel hub. This hub is connected by several spokes to the rim of the wheel, utilizing fasteners such as bolts or screws in order to provide structural rigidity to the assembly. In some cases a metal frame mounting plate or "spider" (so-called due to its arachnid appearance) is installed above the hub with its legs fastened to the wheel above the spokes. The inflator is then mounted upon this spider, which has a central aperture configured to accept at least a portion of the inflator housing. Several variations of this arrangement are illustrated in, for example, U.S. Pat. No. 3,827,715 to Lynch and U.S. Pat. No. 3,895,823 to Stephenson.
In an alternate assembly technique practiced in the prior art, an upper "diffuser" portion of the inflator is inserted through an aperture defined in a supporting frame member from the rear thereof. The inflator unit and the frame member are then oriented in a manner such that several apertures defined in flanged "ear" portions which extend from the generator housing, are aligned with corresponding mounting apertures in the mounting plate. This arrangement thus permits these components to be fastened together by the use of a plurality of securing means, such as bolts, rivets or screws which are passed through the generator mounting "ears" and thereafter through the mounting plate.
Moreover, to retain an air bag in operative association with the inflator device, the bag is normally provided around its mouth portion with a number of reinforced apertures. This portion of the bag is then wrapped around a separate bag retaining ring, having a series of apertures corresponding to those through the bag mouth. The bag and ring assembly is then fastened using a second group of fasteners, to the front face of the mounting plate. Alternately, the bag may simply be sandwiched between a retaining member and the front face of the mounting plate with the fasteners passing through: (1) the mounting plate, (2) the air bag and (3) the retaining member. In either event, a variety of time-consuming, labor intensive fastening operations must be undertaken in order to secure: (1) the inflator to the mounting plate and (2) the air bag to the mounting plate. Securing means, such as, for example, lock nuts, are utilized to prevent loosening of the fasteners which connect the various components in operative alignment.
In addition, to protect the relatively fragile electrical leads which extend out of the bottom, i.e., closure, member of the inflator housing (from the electrically activated ignition squib positioned therein), an additional component known as a "wire shield", is typically screwed or bolted to the rear face of the mounting plate, rearwardly of the inflator unit, during the assembly procedure. The wires are routed through an aperture in the diffuser provided therein for this purpose and thereafter through an open space in the wire shield to a remote collision sensor located elsewhere upon the vehicle. This "wire shield" member, requiring a separate assembly step to install, is required to prevent the wires from breaking off from the squib if the inflator device is accidentally dropped or bumped during its assembly with the mounting plate or during installation within the steering mechanism of the vehicle.
The air bag is normally folded for storage and positioned on top of the diffuser portion of the inflator, which extends above the mounting plate through the mounting aperture, where it remains until the passenger restraint apparatus is actuated. A cover member is then installed above the bag in order to hide the assembly from view and to improve the aesthetic appearance of the vehicle's interior.
To facilitate the installation and removal of airbag systems of the type described above, these assemblies have previously been produced in modular form, as described for example, in U.S. Pat. No. 3,819,205 to Dunford et al. In a preferred embodiment of the Dunford et al. device, a support plate, generally conforming to the shape of the opening of a dished hub, includes extensions which overlie the spokes. Offset flanges on the support member seat on embossments of the hub and are secured thereto by fasteners inserted from the lower side of the hub.
The support plate mounts the gas generator, the diffuser, the air bag, a container for the air bag, and an outer decorative closure which hides the aforementioned components from view. In addition, both the container and the closure are provided with H-shaped weakened, i.e., scored, portions which may be readily ruptured to provide an opening so that the air bag can deploy therethrough when the gas generator is actuated. The assembly of these modularized components still, however, requires the insertion of a plurality of fastener members in order to maintain each part in operative alignment.